Heathrow has revealed how it can deliver a brand-new tunnel and bridges for the M25 while keeping motorists on the move during construction of a third runway.

The new future-proofed section will be built ‘offline’ on land 130 metres to the west of today’s motorway, keeping construction separate from daily commuters.

Traffic will then be switched from the old route to the new using carefully planned overnight closures. Once the new tunnel is complete motorists will benefit from a wider and safer stretch of motorway, 100% privately financed by Heathrow.

It will include new link roads that will separate the passing M25 traffic from those leaving and joining the M4, eliminating weaving movements and offering safer journeys.

Since expanding Heathrow proposals were submitted to the Government, the M25 has been one of the most common questions. Heathrow has a clear plan that will upgrade a key part of the UK’s road network, which has been shaped over years of engagement with National Highways.

Alternative options to place a new runway over the M4 spur were evaluated but discarded by both Heathrow and the Airports Commission for having fewer benefits and causing more disruption.

Any design that avoids the M25, some airlines have indicated, would result in a runway too short to accommodate all long-haul flights. Building over the M4 spur would require the demolition of thousands more homes and expose more residents to noise once operational.

The M4 spur also runs over a crucial rail tunnel that carries Heathrow Express and Elizabeth Line services in and out of Heathrow. With no space to build ‘offline’, it is unclear how construction could take place on this constrained stretch of road without significant disruption to both rail and road users for months on end.

Heathrow’s Surface Access Director, Sophie Chapman, said: 

“Heathrow expansion is a once in a generation opportunity to upgrade our connectivity in the air and on the ground. One of the legacies of our plan will be a 100% privately financed upgrade to one of the busiest stretches of the M25. We have a tested plan for building next to the current motorway that will keep motorists on the move during construction. We have already looked at the alternatives and they simply create more impacts for less benefits so we’re confident we have the best plan available.”

(Pic: Heathrow Airport/YouTube)